U.S. patent application number 10/466699 was filed with the patent office on 2005-01-20 for myoelectrically activated respiratory leak sealing.
Invention is credited to Sinderby, Christer.
Application Number | 20050011519 10/466699 |
Document ID | / |
Family ID | 22992341 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011519 |
Kind Code |
A1 |
Sinderby, Christer |
January 20, 2005 |
Myoelectrically activated respiratory leak sealing
Abstract
The method and system are for sealing/unsealing (regulating)
airway leaks occuring between the ventilator circuit and
respiratory airways during lung ventilatory support in response to
myoelectrical activity of diaphgram. Myolectrical activity of a
patient's respiratory-related muscle is sensed to detect
respiratory effort, and to produce a myoelectrical signal
representative of the sensed muscle myoelectrical activity.
Respiratory flow and pressure can also be measured to produce
respective respiratory pressure and respiratory flow signals. A
logic trigger sealing/unsealing of airway leaks in relation to the
myoelectrical signal, respiratory flow signal and/or respiratory
pressure signal to assist respiration of the patient. The amplitude
of the myoelectrical signal Is compare to a given threshold, and
airway leaks are sealed when the amplitude of the myoelectrical
signal is higher than this threshold. Increment of myoelectrical
signal amplitude can be also detected to trigger the airway leak
regulating device to seal the airway leaks, while decrement of the
myoelectrical signal amplitude can be detected to unseal the airway
leaks and thus permit air evacuation from the patient's lungs.
Inventors: |
Sinderby, Christer;
(Ontario, CA) |
Correspondence
Address: |
FAY KAPLUN & MARCIN, LLP
15O BROADWAY, SUITE 702
NEW YORK
NY
10038
US
|
Family ID: |
22992341 |
Appl. No.: |
10/466699 |
Filed: |
July 30, 2004 |
PCT Filed: |
January 16, 2002 |
PCT NO: |
PCT/CA02/00056 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60261208 |
Jan 16, 2001 |
|
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|
Current U.S.
Class: |
128/204.23 ;
128/205.23; 128/206.21 |
Current CPC
Class: |
A61M 2230/60 20130101;
A61M 16/0415 20140204; A61M 16/044 20130101; A61M 2230/08 20130101;
A61M 16/0409 20140204; A61M 16/04 20130101; A61B 5/389 20210101;
A61M 16/024 20170801; A61M 16/0461 20130101 |
Class at
Publication: |
128/204.23 ;
128/206.21; 128/205.23 |
International
Class: |
A61M 016/00; A62B
007/00 |
Claims
What is claimed is:
1. A method for controlling an air seal between a ventilator air
circuit and a patient's respiratory airways, comprising: sensing
myoelectrical activity of a respiratory-related muscle of the
patient so as to yield at least one myoelectrical signal
representative of respiratory effort of the patient; comparing said
at least one myoelectrical signal to a predetermined value, so as
to determine the highest value therebetween; and modifying the seal
according to the highest value so as to control said leak.
2. A method for controlling an air seal is recited in claim 1,
wherein said respiratory-related muscle is taken from the group
consisting of diaphragm, parasternal intercostal muscles,
sternocleidomatoids, scalenes, and alae nasi.
3. A method for controlling an air seal as recited in claim 2,
wherein said respiratory-related muscle is the diaphragm.
4. A method for controlling an air seal as recited in claim 3,
wherein said myoelectrical activity is sensed in the electrically
active region of said diaphragm (DDR).
5. A method for controlling an air seal as recited in claim 4,
wherein said myoelectrical activity is sensed near the centre of
the DDR.
6. A method for controlling an air seal as recited in claim 5,
further comprising: sensing at least one signal above said DDR and
at least one signal below said DDR, and subtracting these two
signals to yield at least one myoelectrical signal representative
of the respiratory effort of the patient.
7. A method for controlling an air seal as recited in claim 1,
further comprising filtering from said at least one myoelectrical
signal at least one of the following disturbances: motion
artefacts, electrocardiogram (ECG), electrical interference, and
high frequency noise.
8. A method for controlling an air seal as recited in claim 1,
wherein said predetermined value is a predetermined threshold; said
air seal being modified so as to: (a) seal the patient's
respiratory airways when said at least one myoelectrical signal is
said highest value, thereby avoiding gas leaks during respiratory
effort of the patient, and (b) unseal the patient's airways when
said threshold is the highest value, thereby allowing gas leaks
during relaxation of the respiratory effort of the patient.
9. A method for controlling an air seal as recited in claim 8,
wherein two different thresholds are used in (a) and in (b).
10. A method for controlling an air seal as recited in claim 8,
wherein said threshold is predetermined by manual adjustment using
visual feedback.
11. A method for controlling an air seal as recited in claim 8,
wherein said threshold is predetermined automatically by letting
the level be relative to a predetermined noise level.
12. A method for controlling an air seal as recited in claim 1,
further comprising multiplying a current sample of said at least
one myoelectrical signal by a predetermined constant to produce a
multiplied sample; wherein said predetermined value corresponds to
a prior sample of said at least one myoelectrical signal; said air
seal being modified so as to: (a) seal the patient's respiratory
airways when said current sample is said highest value, thereby
avoiding gas leaks during respiratory effort of the patient, and
(b) unseal the patient's airways when said prior sample of said at
least one myoelectrical signal is the highest value, thereby
allowing gas leaks during relaxation of the respiratory effort of
the patient.
13. A method for controlling an air seal as recited in claim 1,
further comprising detecting the level of noise in said at least
one myoelectrical signal; and determining whether the
respiratory-related muscle of the patient is active in relation to
the detected level of noise.
14. A system for controlling an air seal between a ventilator air
circuit and a patient's respiratory airways, comprising: a
controller; a myoelectrical sensor connected to said controller,
said sensor being configured to sense at least one myoelectrical
signal representative of the respiratory effort of the patient; and
a respiratory sealing device connected to said controller and
configured to modify the air seal according to the at least one
sensed myoelectrical signal.
15. A system for controlling an air seal as recited in claim 14,
wherein said respiratory sealing device is in the form of a sealing
balloon.
16. A system for controlling an air seal as recited in claim 15,
wherein said sealing balloon is mounted on a ventilatory assist
tube of the ventilator air circuit; said ventilatory assist tube
including a first lumen in the form of an air passage from the
ventilatory air circuit, and a second lumen in the form of a fluid
passage for fluid communication between said sealing balloon and a
balloon inflation device and pressure control of said balloon.
17. A method for controlling an air seal as recited in claim 16,
wherein two different thresholds are used in (a) and in (b).
18. A system for controlling an air seal as recited in claim 14,
wherein said respiratory sealing device is in the form of a face
mask including a seal pressure lumen.
19. A system for controlling an air seal as recited in claim 14,
wherein said myoelectrical sensor is in the form of an array of
electrodes.
20. A system for controlling an air seal as recited in claim 19,
wherein said array of electrodes is provided with a constant
inter-electrode distance.
21. A system for controlling an air seal as recited in claim 19,
wherein said array of electrodes includes nine electrodes.
22. A system for controlling an air seal as recited in claim 14,
wherein said myoelectrical sensor is mounted on the free end of a
catheter.
23. A system for controlling an air seal as recited in claim 22,
wherein said myoelectrical sensor includes a steel wire wound
around said catheter.
24. A system for controlling an air seal as recited in claim 23,
wherein said wound steel wire is smoothed out by solder.
25. A system for controlling an air seal as recited in claim 22,
wherein said catheter is an oesophageal catheter.
26. A system for controlling an air seal as recited in claim 14,
wherein said myoelectrical sensor is mounted on the free end of a
nasogastric tube.
27. A system for controlling an air seal as recited in claim 19,
further comprising at least one differential amplifier connected to
both said electrodes and said controller.
28. A system for controlling an air seal as recited in claim 27,
wherein said at least one amplifier includes single-ended
amplifiers, allowing monopolar readings.
29. A system for controlling an air seal as recited in claim 27,
wherein said at least one amplifier is connected to said electrodes
via electric wires.
30. A system for controlling an air seal as recited in claim 27,
comprising a differential amplifier for each pair of
electrodes.
31. A system for controlling an air seal as recited in claim 27,
wherein said at least one isolation amplifier is configured for
sampling said at least one myoelectrical signal to form signal
segments.
32. A system for controlling an air seal as recited in claim 14,
wherein said controller is in the form of a personal computer.
33. A system for controlling an air seal between a ventilator air
circuit and a patient's respiratory airways, comprising: means for
sensing myoelectrical activity of a respiratory-related muscle of
the patient; means for modifying the air seal; and means for
controlling the air seal modifying means depending on the sensed
myoelectrical activity.
34. A system as recited in claim 29, further comprising means for
filtering from said at least one myoelectrical signal at least one
of the following disturbances: motion artefacts, ECG, electrical
interference, and high frequency noise.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to ventilatory support
systems. More particularly, the present invention is concerned with
a myoelectrically activated respiratory leak sealing method and
system.
BACKGROUND OF THE INVENTION
[0002] Inherent to methods of administrating ventilatory support
via delivering inspiratory flow, volume, and/or pressure to the
airways is the influence of airway leaks occurring between the
ventilator circuit and respiratory airways. A poor seal between the
device used for administration of ventilatory support (e.g.,
endotracheal tube, face/nasal mask) and the patient (e.g., airway,
airway opening) introduces difficulties to deliver appropriate gas
flow, volume, or pressure into the airway system in order to
inflate the lungs.
OBJECTS OF THE INVENTION
[0003] An object of the present invention is to use myoelectrical
activity of the diaphragm or other respiratory-related muscles to
activate and/or to deactivate a seal in order to regulate leaks
between the ventilator circuit and respiratory airways.
SUMMARY OF THE INVENTION
[0004] A present invention relates to a method and system for
sealing/unsealing airway leaks between the patient's airways and a
ventilatory support apparatus in response to a respiratory effort
via the use of myoelectrical activity of the diaphragm (or other
muscles associated with respiratory effort).
[0005] Methods and systems according to the present invention allow
synchronizing the activation of the seal between the respiratory
airways and ventilator circuit with the neural activation of
inspiratory muscles.
[0006] Methods and systems according to the present invention
further allow to reduce the problems related to the interface and
the leaks occurring between the respiratory airways and ventilator
circuit during the entire (or parts of) the period of neural
inspiratory activation, which help to ensure adequate delivery of
gas flow, volume and/or pressure into the lungs.
[0007] Methods and systems according to the present invention also
allow synchronizing the deactivation of the, seal between the
respiratory airways and ventilator circuit with the neural
deactivation of inspiratory muscles.
[0008] More specifically, according to the present invention, there
is provided a method for controlling an air seal between a
ventilator air circuit and a patient's respiratory airways,
comprising:
[0009] sensing myoelectrical activity of a respiratory-related
muscle of the patient so as to yield at least one myoelectrical
signal representative of respiratory effort of the patient;
[0010] comparing the at least one myoelectrical signal to a
predetermined value, so as to determine the highest value
therebetween; and
[0011] modifying the seal according to the highest value so as to
control the leak.
[0012] According to another aspect of the present invention, there
is provided a system for controlling an air seal between a
ventilator air circuit and a patient's respiratory airways,
comprising:
[0013] a controller;
[0014] a myoelectrical sensor connected to the controller, the
sensor being configured to sense at least one myoelectrical signal
representative of the respiratory effort of the patient; and
[0015] a respiratory sealing device connected to the controller and
configured to modify the air seal according to the at least one
sensed myoelectrical signal.
[0016] According to still another aspect of the present invention,
there is provided a system for controlling an air seal between a
ventilator air circuit and a patient's respiratory airways,
comprising:
[0017] means for sensing myoelectrical activity of a
respiratory-related muscle of the patient;
[0018] means for modifying the air seal; and
[0019] means for controlling the air seal modifying means depending
on the sensed myoelectrical activity.
[0020] Other objects, advantages and features of the present
invention will become more apparent upon reading the following
non-restrictive description of preferred embodiments thereof, given
by way of example only with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] In the appended drawings:
[0022] FIG. 1 is a schematic view of a myoelectrically activated
respiratory leak-sealing system, according to a first embodiment of
the present invention, illustrated on a human patient;
[0023] FIG. 2 is a front elevational view of the myoelectrical
sensor of FIG. 1, according to a first embodiment of the present
invention;
[0024] FIG. 3 is a front elevational view of the myoelectrical
sensor of FIG. 1, according to a second embodiment of the present
invention;
[0025] FIG. 4 is a graph showing a set of EMG signals of the
diaphragm (EMGdi signals) detected by pairs of successive
electrodes of the sensor of FIG. 2;
[0026] FIG. 5 is a cross-sectional view taken along line 5-5 of
FIG. 1;
[0027] FIG. 6 is a schematic view of a respiratory sealing device,
according to a second embodiment of the present invention,
illustrated inserted in a nasal air passage of the patient of FIG.
1;
[0028] FIG. 7 is a schematic view of respiratory sealing device
according to a third embodiment of the present invention,
illustrated mounted on the face of the patient of FIG. 1;
[0029] FIG. 8 is a flow chart of a myoelectrically activated
respiratory leaksealing method according to an embodiment of, the
present invention;
[0030] FIGS. 9a and 9b illustrate a flow chart of step 102 from
FIG. 8;
[0031] FIG. 10a is a graph showing the power density spectrum of
electrode motion artefacts, the power density spectrum of
electrocardiogram (ECG), and the power density spectrum of EMGdi
signals;
[0032] FIG. 10b is a graph showing an example of transfer function
for a filter to be used for filtering out the electrode motion
artefacts, electrocardiogram (ECG), the 50 or 60 Hz disturbances
from electrical mains and high frequency noise;
[0033] FIG. 11a is a graph of inspiratory and expiratory flow
versus time for quiet breathing of a chronic obstructive pulmonary
disease (COPD) patient;
[0034] FIG. 11b is a graph of the RMS value of EMG versus time for
quiet breathing of a COPD patient, the graphs of FIGS. 10a and 10b
showing the time delay from EMG to airway inspiratory flow;
[0035] FIG. 12 is a graph showing the distribution of correlation
coefficients calculated for determining the position of the centre
of the depolarizing region of the diaphragm along the array of
electrodes of FIG. 2;
[0036] FIG. 13 is a schematic view with graphs illustrating, in the
time domain, a double subtraction technique for improving the
signal-to-noise ratio and to reduce an electrode-position-induced
filter effect;
[0037] FIG. 14 is a schematic diagram, illustrating in the
frequency domain, stabilization by the double subtraction technique
of the centre frequency upon displacement of the centre of the
depolarizing region of the diaphragm of FIG. 1 along the array of
electrodes of FIG. 2; and
[0038] FIG. 15a is a graph of oesophageal and gastric pressure
versus time for quiet breathing of a chronic obstructive pulmonary
disease (COPD) patient; and FIG. 15b is a graph of the RMS value of
EMG versus time for quiet breathing of a COPD patient; the graphs
of FIGS. 15a and 15b show the relation between EMG and the
oesophageal and gastric pressure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0039] Turning to FIG. 1 of the appended drawings, a
myoelectrically activated respiratory leak sealing system 10
according to a first embodiment of the present invention is
illustrated.
[0040] The system 10 comprises a myoelectrical sensor 12 mounted on
the free end section 14 of an oesophageal catheter 16, a
respiratory sealing device in the form of a sealing balloon 18, and
a controller 20.
[0041] As illustrated in FIG. 2, the myoelectrical sensor 12 is in
the form of an array of electrodes 22 provided with a constant
inter-electrode distance d, and allows measuring the
electromyographic (EMG) activity of the diaphragm 24 (EMGdi) of a
patient 26.
[0042] The electrodes 22 are mounted on the free end section 14 of
the catheter 16 by winding stainless steel wire (not shown) around
the catheter 16. The wound stainless steel wire presents a rough
surface smoothed out by solder, which in turn is electroplated with
nickel, copper and then gold or silver. Of course, it is within the
scope of the present invention to use other electrode
structures.
[0043] In the embodiment illustrated in FIGS. 1 and 2, the free end
section 14 of the catheter 16 is provided with an array of eight
electrodes 22 defining seven pairs 1, 2, 3, 4, 5, 6 and 7 of
successive electrodes 22 respectively collecting seven different
EMGdi signals.
[0044] Although it has been found that EMG activity of the
diaphragm (EMGdi) can be measured accurately with an oesophageal
catheter 16 provided on the free end section 14 thereof with an
array of eight electrodes 22, a different number and/or
configuration of pairs of electrodes 22 can be contemplated
depending on the patient's anatomy and movement of the diaphragm
24. Also, the pairs 1-7 do not need to be pairs of successive
electrodes; FIG. 3 illustrates an array of nine electrodes to form
seven overlapping pairs of electrodes 1'-7'.
[0045] Alternatively, the electrodes 22 can possibly be applied to
a nasogastric tube (not shown), which is routinely introduced in
intensive-care unit (ICU) patients.
[0046] Electric wires (not shown) interconnect each pair of
successive electrodes such as 1-7 (FIG. 2) with a respective one of
a group of differential amplifiers 30 (FIG. 1). Obviously, these
electric wires follow the catheter 16 from the respective
electrodes 22 to the corresponding amplifiers 30, and are
preferably integrated to the catheter 16.
[0047] The electric wires transmitting the EMGdi signals collected
by the various pairs 1-7 of electrodes 22 are shielded to reduce
the influence of external noise, in particular disturbance from the
50 or 60 Hz current and voltage of the electrical mains.
[0048] The group of differential amplifiers 30 amplifies (first
subtraction step of the double subtraction technique that will be
described hereinbelow) and band-pass filters each EMGdi signal.
This first subtraction step may also be carried out in the
controller, which is in the form of a personal computer 20, when
the amplifiers 16 are single-ended or equivalently designed
amplifiers (monopolar readings).
[0049] A common problem in recording EMGdi signals is to maintain
the noise level as low and as constant as possible. Since the
electric wires transmitting the EMGdi signals from the electrodes
22 to the differential amplifiers 30 act as an antenna, these
electric wires are shielded to thereby protect the EMGdi signals
from additional artefactual noise. Also, the package enclosing the
differential amplifiers 30 is preferably made as small as possible
(miniaturized) and is positioned in close proximity to the
patient's nose to decrease as much as possible the distance between
the electrodes 22 and the amplifiers 30.
[0050] The personal computer 20 allows sampling the amplified EMGdi
signals through respective isolation amplifiers of a unit 32, to
form signal segments of fixed duration. Unit 32 supplies electric
power to the various electronic components of the differential and
isolation amplifiers while ensuring adequate isolation of the
patient's body from such power supply. The unit 32 also
incorporates bandpass filters included in the respective EMGdi
signal channels to reduce the effects of aliasing. The successive
EMGdi signal segments are then digitally processed into the
personal computer 20 after analog-to-digital conversion thereof. An
analog-to-digital converter implemented in the personal computer 20
conveniently carries out this analog-to-digital conversion.
[0051] It is believed to be within the capacity of those of
ordinary skill in the art to construct suitable differential
amplifiers 30 and adequate isolation amplifiers and power supply
unit 32. Accordingly, the amplifiers 30 and the unit 32 will not be
further described in the present specification.
[0052] As shown in FIG. 1, the catheter 16 is introduced into the
patient's oesophagus through one nostril or the mouth until the
array of electrodes 22 is situated at the level of the
gastroesophageal junction. Since the diaphragm 24 and/or the
oesophagus slightly moves during breathing of the patient 26, the
array of electrodes 22 also slightly moves about the diaphragm 24.
As will be explained in the following description, automatic
compensation for this displacement is advantageously provided
for.
[0053] An example of the seven EMGdi signal components (hereinafter
EMGdi signals) collected by the pairs 1-7 of successive electrodes
22 (FIGS. 1 and 2) and supplied to the computer 20 is illustrated
in FIG. 4.
[0054] The sealing balloon 18 (FIG. 1) is mounted on a ventilatory
assist tube 34 thereabout.
[0055] The tube 34 is an endotracheal tube that is to be inserted
in the trachea 36 of the patient 26 via the mouth or the nose or
tracheotomy. The tube 34 is part of the ventilator air circuit of a
conventional ventilatory assistance system and is therefore
connected to ventilator assist and sealing balloon controllers
(both not shown).
[0056] As shown in FIG. 5, the ventilator assist tube 34 comprises
two lumens: a ventilator assist lumen 38 and a seal pressure
control lumen 40. The ventilatory assist lumen 48 is an air passage
from the ventilator assist device (not shown) and the patient's
lungs. The seal pressure control lumen 40 is an air or fluid
passage from a balloon inflation device (not shown) to the sealing
balloon 18 or mask 46 (see FIG. 7). The balloon inflation device
can be any device providing a known volume or a known pressure.
[0057] The sealing balloon controller is connected to the computer
20 and its operation is controlled thereby.
[0058] In operation, the ventilatory endotracheal ventilatory
assist tube 34, with the sealing balloon 18 integrally mounted
thereto, are inserted in the trachea 36 of the patient 26 via the
mouth or the nose or tracheotomy. The oesophageal catheter 16 with
the myoelectrical sensor 12 are introduced into the patient's
oesophagus through one nostril or mouth until the array of
electrodes 22 is located at the level of the gastroesophageal
junction.
[0059] As will be explained in further detail hereinbelow, upon
inspiration of the patient 26, the change in EMG activity of the
diaphragm 24 is detected by the sensor 12 and the detected signal
is analysed by the computer 20 that commands the balloon controller
to inflate the sealing balloon 18, thereby providing an air seal
between the ventilatory assist tube 34 and the patient's
respiratory airways (the trachea 36 in this exemplary embodiment).
Upon expiration of the patient 26, the sensor 12 detects the change
in EMG activity of the diaphragm 24 and the computer 20 commands
the balloon controller to deflate the balloon 18, thereby allowing
gas leaks around the ventilatory assist tube 34.
[0060] FIGS. 6 and 7 show two alternative embodiments of
respiratory sealing devices.
[0061] In the embodiment of FIG. 6, the sealing balloon 18' is so
mounted to the ventilatory assist tube 34 as to be located, in
operation, in the nasal passage 42 of the patient 26. In operation,
upon inspiration of the patient 26, the sealing balloon 18'
inflates, thereby providing an air seal between the ventilatory
assist tube 34 and the patient's respiratory airways (the nasal
passage 42 in this exemplary embodiment). Upon expiration of the
patient 26, the sealing balloon 18' will deflate, thereby allowing
gas leaks around the ventilatory assist tube 34, and also giving
the patient 26 the ability to speak.
[0062] FIG. 7 shows the human patient 26 with a ventilatory assist
facemask 44 over its mouth and nose. The facemask 44 is connected
to the ventilatory assist tube 34. The ventilator assist tube 34 is
in turn connected to ventilator assist and sealing balloon
controllers (both not shown). In this particular embodiment, a seal
46 is provided at the edge portion of facemask 44. The seal 46 is
fluidly connected to a ventilator assist tube seal pressure control
lumen 40 (FIG. 5) through the facemask seal pressure control lumen
48. Upon inspiration of the patient 26, the seal 46 inflates,
thereby providing an air seal between the facemask 44 and the
patient's respiratory airways (the patient's mouth and nose in this
exemplary embodiment). Upon expiration of the patient 26, the seal
46 deflates, thereby allowing gas leaks around the facemask 62.
[0063] Other features of the system 10 will become more apparent
upon reading the following description of a myoelectrically
activated respiratory leak sealing method 100, according to an
embodiment of the present invention. As will now be described in
more detail, the method 100 allows controlling the air seal 18.
[0064] Generally stated, the method 100 comprises the following
steps:
[0065] 102--sensing the myoelectrical activity of the diaphragm
24;
[0066] 104--comparing the myoelectrical signal to a predetermined
value; and
[0067] 106--modifying the state of the sealing device 18 according
to the comparison result in step 104.
[0068] Each of these steps will now be described in further
detail.
[0069] In step 102, the myoelectrical activity of the diaphragm is
measured using sensor 12. The objective is to provide a
myoelectrical signal representative of the respiratory effort of
the patient 26.
[0070] More specifically, a crural diaphragm EMG is recorded from a
sheet of muscle whose fibre direction is generally perpendicular to
an oesophageal bipolar electrode. The region from which the action
potentials are elicited, the electrically active region of the
diaphragm (DDR), and the centre of this region, the DDR centre, may
vary during voluntary contractions, in terms of their position with
respect to an oesophageal electrode. Depending on the position of
the bipolar electrode with respect to the DDR centre, the EMGdi
signal is filtered to different degrees.
[0071] Based on experimental results and anatomical descriptions of
the crural diaphragm, a transfer function for diaphragm EMG
measured 1 Perpendicularfiltering ( K 0 ( ( h - d ) / v ) - K 0 ( (
h + d ) / v ) ) 2 K 0 2 ( a / v )
[0072] with bipolar electrodes, such as electrodes 22, has been
developed where, K( )=modified Bessel function, .omega.=angular
frequency (i.e. 2.pi.f (f being the frequency), h=distance between
the signal source and observation point, d=1/2 inter-electrode
distance, v=conduction velocity, a=muscle fiber diameter.
[0073] Based on this transfer function, a signal analysis procedure
has been developed which involves:
[0074] (a) locating the electrode pair at the centre of the
diaphragm depolarizing region (DDR) (this region will be defined
hereinbelow);
[0075] (b) selecting the signals above and below the centre of the
DDR (reversed in polarity) yielding the highest signal-to-noise
ratio; and
[0076] (c) subtracting these two signals (double subtraction
technique).
[0077] The double subtraction technique allows to reduce the
influence of movement of the DDR centre relative to the electrode
array 12 on the EMG power spectrum centre frequency and root mean
square values, to increase the signal to noise ratio by 2 dB, and
to increase the number of EMG samples that are accepted by the
signal quality indices by 50%. A more detailed description of the
above mentioned double subtraction technique is given
hereinbelow.
[0078] Step 102 will now be described in further detail with
reference to FIG. 9.
[0079] The first operation (substep 202) performed by the computer
20 is a filtering operation to remove from all the EMGdi signals of
FIG. 4 electrode motion artefacts, ECG, 50 and 60 Hz interference
from the electrical network, and high frequency noise. The graph of
FIG. 10a shows the power density spectrum of the above defined
electrode motion artefacts, the power density spectrum of ECG, and
the power density spectrum of EMGdi signals.
[0080] It is to be noted that motion artefacts are induced by
motion of the electrodes 22. More generally, motion artefacts are
defined as a low frequency fluctuation of the EMGdi signals' DC
level induced by mechanical alterations of the electrode metal to
electrolyte interface i.e. changes in electrode contact area and/or
changes in pressure that the tissue exerts on the electrode.
[0081] The influence of ECG on the EMGdi signals can be suppressed
or eliminated in different ways. Depending on the working mode,
i.e. on-line or off-line analysis, time domain or frequency domain
processing, different optimal signal conditioning methods can be
chosen. In time-critical applications, an optimized filtering has
been found advantageous.
[0082] FIG. 10b presents an optimal filter transfer function to
isolate the EMGdi from a compound signal including ECG and also
disturbed by background noise and electrode motion artefacts. In
FIG. 10b, the dashed line shows the optimal transfer function,
while the solid line shows the transfer function implemented by the
inventors. FIG. 10b is therefore an example of filter transfer
function that can be used in substep 202 for filtering out the
electrode motion artefacts, ECG, the 50 or 60 Hz disturbance from
the electrical mains, and the high frequency noise. Processing of
the EMGdi signals by the computer 20 to follow, as closely as
possible, the optimal transfer function of FIG. 10b will provide
adequate filtering in substep 202.
[0083] An example of integrated EMGdi signal from a chronic
obstructive pulmonary diseased (COPD) patient in relation to
oesophageal and gastric pressure is depicted in FIGS. 10a and
10b.
[0084] Substep 204 involves the determination of the position of
the centre of the DDR.
[0085] As the diaphragm is generally perpendicular to the
longitudinal axis of the oesophageal catheter 16 equipped with an
array of electrodes 22, only a portion of the electrodes 22 are
situated in the vicinity of the diaphragm 24. Determining the
position of the diaphragm 24 with respect to the oesophageal
electrode array 12 therefore provides for better results.
[0086] The portion of the crural diaphragm 24, which forms the
muscular tunnel through which the oesophageal catheter 16 is
passed, is referred to the "diaphragm-depolarizing region" (DDR).
The thickness of the DDR is about 20-30 mm. It is assumed that,
within the DDR, the distribution of active muscle fibres has a
centre from which the majority of the EMGdi signals originate, i.e.
the "diaphragm-depolarizing region centre" (DDR centre). Therefore,
EMGdi signals detected on opposite sides of the DDR centre will be
reversed in polarity with no phase shift; i.e. EMGdi signals
obtained along the electrode array 12 are reversing in polarity at
the DDR centre.
[0087] Moving centrally from the boundaries of the DDR, EMGdi power
spectrums progressively attenuate and enhance in frequency.
Reversal of signal polarity on either side of the electrode pair 4
with the most attenuated power spectrum confirms the position from
which the EMGdi signals originate, the DDR centre.
[0088] In step 204 of FIG. 9a, the position of the centre of the
DDR along the array of electrodes 22 is determined.
[0089] The centre of the DDR is repeatedly updated, that is
re-determined at predetermined time intervals. For that purpose,
the EMGdi signals are cross-correlated in pairs in substep 204a to
calculate cross-correlation coefficients r. As well known to those
skilled in the art, cross-correlation is a statistical
determination of the phase relationship between two signals and
essentially calculates the similarity between two signals in terms
of a correlation coefficient r. A negative correlation coefficient
r indicates that the cross-correlated signals are of opposite
polarities.
[0090] FIG. 12 shows curves of the value of the correlation
coefficient r versus the midpoint between the pairs of electrodes
22 from which the correlated EMGdi signals originate. In this
example, the inter-electrode distance d is 10 mm. Curves are drawn
for distances between the correlated pairs of electrodes 22 of 5 mm
(curve 52), 10 mm (curve 54), 15 mm (curve 56) and 20 mm (curve
58). One can appreciate from FIG. 12, that negative correlation
coefficients r are obtained when EMGdi signals from respective
electrode pairs situated on opposite sides of the electrode pair 4
are cross-correlated. It therefore appears that the change in
polarity occurs in the region of electrode pair 4, which is
confirmed by the curves of FIG. 4. Accordingly, it can be assumed
that the centre of the DDR is situated substantially midway between
the electrodes 22 forming pair 4.
[0091] In substep 204b, the correlation coefficients are
systematically compared to determine the centre of the DDR. For
example, the centre of the DDR can be precisely determined by
interpolation using a square law based fit of the three most
negative correlation coefficients of curve 54 from FIG. 12 obtained
by successive cross-correlation of the EMGdi signal segments from
each electrode pair to the EMGdi signal segments from the second
next electrode pair. Association of the centre of the DDR to a pair
of electrodes 22 provides a "reference position" from which to
obtain EMGdi signal segments within the DDR.
[0092] As mentioned in the foregoing description, the position of
the DDR centre along the array of electrodes 22 is continuously
updated, i.e. re-calculated at predetermined time intervals
overlapping or not. In substep 204c, update of the position of the
DDR centre is controlled by comparing the most negative correlation
coefficient r.sub.NEG to a constant K3 (substep 204d). If
r.sub.NEG<K3, it is considered that the EMGdi signal represents
the diaphragm 24 and the position of the centre of the DDR is
updated (substep 204e); if r.sub.NEG>K3, it is considered that
the EMGdi signal does not represent the diaphragm 21 and the
position of the centre of the DDR is not updated (substep 204f).
The control carried out in substep 204c allows overcoming the
artefactual influence on the EMGdi power spectrum or signal
strength measurement.
[0093] It has been experimentally demonstrated that EMGdi signals
recorded in the oesophagus of adults are satisfactory as long as
they are obtained from electrode pairs (with an inter-electrode
distance situated between 5 and 20 mm) positioned at a distance
situated between 5 and 30 mm on the opposite sides of the DDR
centre (the inter-pair distance being therefore situated between 5
and 30 mm). With infants, this may change. Although EMGdi signals
obtained from these positions offer a clear improvement in
acceptance rates, the signal-to-noise ratio during quiet breathing
still tends to remain unsatisfactorily low.
[0094] For example, in FIG. 4, the EMGdi signals originating from
the electrode pairs 3 and 5, situated respectively 10 mm below and
10 mm above the DDR, are strongly inversely correlated at zero time
delay. In contrast to the inversely correlated EMGdi signals, the
noise components for electrode pairs 3 and 5 are likely to be
positively correlated. Hence, as illustrated in FIG. 13,
subtraction of the EMGdi signals 60 and 62 from electrode pairs 3
and 5 will result in an addition of the corresponding EMGdi signals
(see signal 64) and in a subtraction, that is, an elimination of
the common noise components. This technique is referred to as "the
double subtraction technique".
[0095] This second subtraction step of the double subtraction
technique can be carried out either in the time domain, or after
conversion of signals 60 and 62 into the frequency domain. A double
subtraction technique can be performed by subtracting other
combinations of signals, or by altering the polarities of electrode
pairs. Two signals of opposite polarities obtained in the vicinity
of the muscle on opposite sides of the DDR are subtracted, or if
polarity is altered, on opposite sides of the DDR, to add signals
from opposite sides of the DDR.
[0096] Therefore, double-subtracted signal segments 206 are
obtained at the output of step 206a by subtracting the EMGdi signal
segments from the pair of electrodes 22 in optimal location above
the diaphragm 24 from the EMGdi signal segments from the pair of
electrodes 22 in optimal location below the diaphragm 24.
[0097] The double subtraction technique compensates for the changes
in signal strength and frequency caused by movement of the
diaphragm 24 (FIG. 1) and/or the oesophagus during breathing of the
patient 26 causing movement of the array of electrodes 22 with
respect to the diaphragm 24.
[0098] Referring to FIG. 14, off centre of the array of electrodes
22 (electrode-position-induced filter effect) causes a variation of
centre frequency values (see curves 66 and 68) for the EMGdi
signals from the electrode pairs 3 and 5. The double subtraction
technique eliminates such variation of centre frequency values as
indicated by curve 70 as well as variation of signal strength.
Therefore, the reciprocal influence of the position of the DDR
centre on the EMGdi signal frequency content is eliminated by the
double subtraction technique.
[0099] It has been found that the double subtraction technique may
improve the signal-to-noise ratio by more than 2 dB and reduce an
electrode-position-induced filter effect. Double subtraction
technique also allows for a relative increase in acceptance rates
by more than 50%.
[0100] Cross-talk signals from adjacent muscles are strongly
correlated at zero time delay and equal in polarity between all
pairs of electrodes 22. Hence, these cross-talk signals appear as a
common mode signal for all electrode pairs and therefore, are
eliminated by the double subtraction technique.
[0101] In substep 206, the strength of the EMGdi signal is
calculated. In substep 206a, a pair of EMGdi signals (signals 1-7
of FIG. 4) obtained from electrode pairs above and below the DDR
centre are subtracted from each other and the RMS
(Root-Mean-Square) value of the resulting signal is calculated and
referred to as RMSsub (substep 206c). Measures of signal intensity,
other than the RMS value, can also alternatively be used.
[0102] In a substep 206b, the above mentioned pair of EMGdi signals
(see signals 1-7 of FIG. 4), obtained from electrode pairs above
and below the DDR centre, are added to each other and the RMS
(Root-Mean-Square) value of the resulting addition signal is
calculated and referred to as RMSadd (substep 206d). Measures of
signal intensity other than the RMS value can also potentially be
used.
[0103] In substep 208, a sufficient increment of the RMS signal
amplitude RMSsub is detected. More specifically, in substep 208a,
the RMS amplitude RMSsubn of the last EMGdi subtraction signal
segment, as calculated by substep 206c, is compared with the
RMSsubn-1 of EMGdi subtraction signal segment last accepted in
substep 210c. If (RMSsubn.times.K1)<RMSsubn-1- , no increment is
detected and the system will wait until analysis of the next EMGdi
subtraction signal segment is performed. On the contrary, if
(RMSsubn.times.K1)>RMSsubn-1, an increment of the RMS intensity
of the EMGdi signal is detected and detection of the common mode
influence (substep 210) is activated. Of course, the multiplication
operation (.times.K1) can be replaced by other suitable
mathematical operations conducted on either the term RMSsubn or
RMSsubn-1.
[0104] Substep 210 enables detection of signal artefacts of
non-diaphragmatic origin. As indicated in the foregoing
description, EMGdi signals generated by the diaphragm and recorded
on either side of the diaphragm 24 will have reversed polarity and
no time delay. Accordingly, a subtraction signal, representative of
the difference between these two EMGdi signals, will have a larger
amplitude than an addition signal representing the sum of such
EMGdi signals. In contrast, signals generated away from, and on the
same side of the diaphragm 24, will have the same polarity on all
electrode pairs and no time delay. As well, signals from the heart
that are not obtained with electrode pairs located too far apart
will have a similar shape but will have a time delay. Differing
from signals with reversed polarity, subtracted signals with the
same polarity will have smaller amplitudes than added signals.
Hence the ratio or difference between the sum and difference
between signals obtained from the same electrode pairs on either
side of the diaphragm can indicate if a signal is of a diaphragm or
an artefactual origin.
[0105] For that purpose, in substep 210b, the amplitude RMSsubn is
compared with the amplitude RMSaddn multiplied by a constant K2. It
is to be noted that the indicia "n" is representative of the last
EMGdi subtraction or addition signal segment. If
RMSsubn<(RMSaddn.times.K2), the RMS signal amplitude is rejected
(substep 210a ) and the two EMGdi signals are considered to have an
artefactual origin. If RMSsubn>(RMSaddn.times.K2), the RMS
signal amplitude is accepted (substep 210c) and the two EMGdi
signals are considered to have a diaphragm origin. Of course, the
multiplication operation (.times.K2) can be replaced by other
suitable mathematical operations conducted on either the term
RMSsubn or RMSaddn.
[0106] In EMGdi signal replacement substep 216, a substep 216a
determines whether the last RMS signal amplitude is accepted. If
the last RMS signal amplitude is accepted, RMSsubn is kept (substep
216a). If the last RMS signal amplitude is not accepted, RMSsubn is
replaced by RMSsubn-1 or with another prediction (substep
216c).
[0107] An increase in amplitude of RMSsubn does not necessarily
mean that the diaphragm 24 is the signal source. It is therefore
advantageous to discriminate signals originating from the diaphragm
24 from signals of other origins. In the foregoing description, it
has been described that a technique of sequential cross-correlation
of the EMGdi signals from pairs of electrodes 22 can be used to
determine the location of the diaphragm by the most negative
correlation coefficient rNEG. Other simplified calculations of
correlation can be used. The magnitude of the correlation
coefficient rNEG is characteristic of each subject but is typically
negative when the diaphragm is active. If the diaphragm is not
active, the negative correlation coefficient rNEG is very low or
the correlation coefficient is positive. The onset of diaphragm
activation can therefore be detected through the amplitude of the
correlation coefficient rNEG.
[0108] To determine the mean level of noise RMSsubNOISE (step 218),
a mean amplitude of RMSsubn is calculated. For that purpose, when
rNEG>K4, K4 being a constant, this indicates that the diaphragm
is not active (substep 218a) and the mean level of RMSsubn, i.e.
RMSsubNOISE is calculated (substep 218b) and outputted. If
rNEG<K4, the system 10 remains in an idle state (step 218c).
[0109] An alternative to substep 218 is to detect the onset of
inspiration through detection of airway inspiratory flow.
[0110] Even though step 102 has been described by referring to the
measurement of the myoelectrical activity of the diaphragm 24 using
the system 10, the measurement of other respiratory-related EMG can
be obtained with a suitable device placed in the vicinity of the
respiratory-related muscle, inserted or implanted on the surface of
or into the muscle of interest.
[0111] Furthermore, other increases in EMGdi signal amplitude, its
integrals or derivatives or combinations thereof, detected via an
EMG recording of the diaphragm or other muscles associated with
inspiration above a desired threshold level, and exceeding a
desired duration, can be used to indicate the onset of an
inspiratory effort.
[0112] The magnitude of the signal itself may also be used. The
signal can be applied, for example, in proportion to the signal
times a constant and its maximum value up to a certain pressure or
volume level.
[0113] After a myoelectrical signal representative of the
inspiratory effort of the patient 26 has been obtained, this signal
is compared, in step 104, to a predetermined threshold so as to
determine the highest value therebetween, and to send a control
command to the respiratory sealing device 18 so as to modify the
state of the sealing device according to a comparison result (step
106).
[0114] Determination of the level to be exceeded (threshold) in
terms of amplitude and duration can either be performed by manual
adjustment supervised via visual feedback, or by automatically
letting the level be relative to the above described mean noise
level. An algorithm can further be used to trigger the respiratory
sealing device 18 when the amplitude of an EMG signal segment of
defined duration exceeds the threshold.
[0115] The duration of time that the EMG amplitude remains above
the threshold level can be used to decide the duration of the
breath e.g. the ventilatory support system can start and deliver a
full breath independent of the presence of EMG activity that
exceeds the threshold level. The algorithm can also be adjusted to
discontinue the ventilatory support if the EMG amplitude drops
below the threshold level, or in response to a decrease in
amplitude that exceeds a given magnitude (decrement).
[0116] In step 104, the RMS amplitude RMSsubn may be compared to a
predetermined parameter P5.
[0117] If RMSsubn>P5, the RMS amplitude is higher than the
threshold P5 and the sealing device 18 is activated so as to seal
the air leak to avoid gas leaks during the respiratory effort of
the patient 26.
[0118] If, on the other hand, RMSsubn<P5 the RMS amplitude is
below the threshold P5, and the sealing device 18 is activated so
as to unseal the air leak to allow gas leaks during the relaxation
of the patient's respiratory effort. P5 is a parameter equal to
RMSsub.sub.NOISE.times.K7, K7 being a predetermined constant. It is
to be noted that the parameter P5 would normally be different for
triggering on and triggering off the sealing device 18 since the
noise level is different in both cases.
[0119] Again, the multiplication operation (.times.K7) can be
replaced by other suitable mathematical operations conducted on
term RMSsub.sub.NOISE.
[0120] Alternatively or additionally to the comparison between the
myoelectrical signal corrected amplitude RMSsub to a predetermined
threshold, a RMSsub amplitude increment and decrement detection can
be performed. The predetermined value to which the amplitude is
compared is, in this particular case, a prior measured and
corrected signal amplitude.
[0121] The prior value RMSsubn-1 is compared to (RMSsubn.times.K6).
If (RMSsubn.times.K6)<RMSsubn-1, the sealing device 18 remains
in an idle state. If (RMSsubn.times.K6)>RMSsubn-1, this
indicates an increment of the RMS amplitude, and sealing of the air
leak by the sealing device 18 is requested through an increment
counting/integrating to support the patient 26. The multiplication
operation (.times.K6) can be replaced by other suitable
mathematical operations conducted on either the term RMSsubn or
RMSsubn-1.
[0122] The function of the increment counting/integrating substep
is to determine the time/magnitude response. The increment signal
is averaged to adjust to sensitivity.
[0123] The prior value RMSsubn-1 is also compared to
(RMSsubn.times.(1/K6)). If (RMSsubn.times.(1/K6))>RMSsubn-1, the
sealing device 18 remains in an idle state. If
(RMSsubn.times.(1/K6))<- RMSsubn-1, this indicates a decrement
of the RMS amplitude and unsealing of the air leak is performed via
the sealing device 18 through a decrement counting/integrating
step. Of course, the multiplication operation (.times.(1/K6)) can
be replaced by other suitable mathematical operations conducted on
either the term RMSsubn or RMSsubn-1.
[0124] The function of the decrement counting/integrating step is
to determine the time/magnitude response. The decrement signal is
averaged to adjust to sensitivity.
[0125] In response to EMG signals, airway inspiratory flow and/or
pressure control commands are sent by the computer 20 for
triggering a ventilatory support system (ventilator) through an
interface (not shown). Indeed, the system 10 advantageously
comprises a digital-to-analog converter and/or other means for
analog and digital interface.
[0126] The decision for triggering will be made by a logic circuit
on a "first come, first serve" basis. For example, if the diaphragm
EMG (or EMG of other inspiratory related muscle) indicates an
inspiratory effort before airway inspiratory flow and/or pressure
indicates the onset of inspiration, the ventilatory support will be
engaged. In the same fashion, the ventilatory support will be
initiated if the inspiratory effort is detected by a threshold for
airway inspiratory flow and/or pressure being exceeded before the
EMG threshold is exceeded.
[0127] Other changes in airway inspiratory flow and/or pressure,
its integrals or derivatives or combinations thereof, in the
inspiratory direction beyond a desired threshold level and detected
via the inspiratory and/or expiratory lines can be used to indicate
the onset of an inspiration.
[0128] The graphs in FIGS. 10a and 10b show, in the case of the
quiet breathing of a COPD patient, that an EMG RMS signal will be
detected approximately 200 ms prior to the onset of airway
inspiratory flow. The graphs in FIGS. 11a and 11b show, still in
the case of the quiet breathing of a COPD patient, a similar
relation between EMG RMS signal and the gastric and oesophageal
pressure. In this particular example, sealing/unsealing in response
to an EMG will enable the airleak regulating device to assist the
patient directly at the onset of inspiration occurring 200 ms after
detection of an EMG RMS amplitude signal.
[0129] The method and device according to the invention is
applicable to all patients (adults and infants) on ventilatory
support and can enhance the possibilities of obtaining spontaneous
breathing and optimizing patient ventilator interaction. The method
and device applies to many kinds of ventilatory support systems
used in intensive care unit settings and other wards where assisted
ventilation is applied, and to other respiratory sealing devices
(also referred to as an air leak regulating device).
[0130] It is to be noted that substeps 204 and 210 of FIG. 9 are
part of the double subtraction technique and are therefore not
necessarily executed with other signal analysis techniques.
Moreover, substep 210 is optional even when using the double
subtraction technique.
[0131] Alternatively, the operation of a system according to the
present invention can be based on the amplitude of the signals or
the area under the curve (integration) of these signals, or other
measures of signal strength.
[0132] Although the preferred embodiment of the present invention
will be described in relation to the use of an EMGdi signal
obtained by means of a double subtracted signal, and representative
of the myoelectrical activity of the diaphragm, it should be kept
in mind that it is within the scope of the present invention to use
another type of EMGdi signal, or to use a signal representative of
the myoelectrical activity of muscles other than the diaphragm, yet
associated with inspiratory effort to trigger the ventilatory
support apparatus. Examples of other muscles are parasternal
intercostal muscles, sternocleidomatoids, scalenes, alae nasi, etc.
The myoelectrical activity of these muscles can eventually be
detected by means of electrodes directly implanted in the
muscle.
[0133] Although the present invention has been described
hereinabove by way of preferred embodiments thereof, it can be
modified without departing from the spirit and nature of the
subject invention, as defined in the appended claims.
* * * * *